Field of the Invention
The present invention relates to poreless ceramics which have excellent optical transmission properties.
Description of the Prior Art
Generally, poreless ceramics have excellent thermal, electrical, chemical and optical properties. Transparent ceramic materials can be used in the fabrication of, for example, crystron tubes, power tubes, antenna windows, integral circuit substrates, high pressure gas-discharge tubes, rocket nozzles, and the like. Currently, many transparent ceramic materials such as Al.sub.2 O.sub.3, MgO, Y.sub.2 O.sub.3, BeO, Gd.sub.2 O.sub.3, LiAl.sub.5 O.sub.8, CaO, ThO.sub.2, MgAl.sub.2 O.sub.5, (Pb,La) (Ti,Zr)O.sub.3 and the like, are known. However, the conventional transparent ceramic materials all have problems concerning their dielectric constants and thermal constants. In addition, the conventional ceramic materials have to be fabricated under hot pressing conditions or special sintering atmospheres and at high sintering temperatures of about 2000.degree. C. Therefore, the cost of these materials becomes expensive because of the necessity of indispensible, complicated facilities and because of difficulties in manufacturing.
A need, therefore, continues to exist for a ceramic material which is inexpensive to prepare and which possesses good optical transmission characteristics and dielectric properties.